1. Field of the Invention
The present invention relates to an overvoltage protection power supply circuit, and more particularly to an overvoltage protection power supply circuit for protecting a flat panel display element of the type installed in laptop type computer systems and the like, such as a PDP (Plasma Display Panel), LCD (Liquid Crystal Display), CCFT (Cold Cathode Fluorescent Tube) or El display (Electroluminescence display), from an overvoltage occurring in the power supply therefor.
2. Description of the Related Art
Generally, existing overvoltage protection power supply circuits for preventing an overvoltage from being applied to a flat panel display element were inadequate. Such overvoltage protection circuits are employed in laptop type computer systems and the like, which require considerably high AC voltage. The overvoltage protection circuit protects the display elements from overvoltage.
Conventionally, the prior overvoltage protection power supply circuits for flat panel display elements were made up of a voltage regulator for outputting regulated DC voltage from an unregulated DC voltage applied to the input terminal, a DC to AC converter for outputting AC voltage from a DC input voltage applied thereto (for example by use of a Hartly Oscillator), and a circuit for removing an overvoltage when the AC output voltage output from the converter is higher than a predetermined voltage. The overvoltage circuit prevents the overvoltage from being applied to the flat panel display elements.
However, the above-mentioned prior protection circuits above are only able to prevent an overvoltage which is higher than a predetermined Zener voltage because Zener diodes were typically installed in front of the output terminal. Moreover, if several Zener diodes are connected in series so as to increase the Zener voltage, the total voltage tolerance is increased in accordance with the numbers of Zener diodes connected in series, and circuit precision suffers. Moreover it is difficult to get a proper Zener diode having a higher Zener voltage.
Also, in the prior art, power consumption by the overvoltage protecting circuit increased when an overvoltage was applied to input terminal because the flow of current through the Zener diodes was increased, with the result that life expectancy of the power supply circuit was shorter. In addition, the prior art overvoltage protection power supply circuits lack continuous protection countermeasures for protecting from overvoltages that cause a current surge which destroys the Zener diodes in the event that they are incapable of enduring the current, thereby exposing both the circuit and the display elements to the overvoltage.